This disclosure relates generally to a concentric airfoil assembly and, more particularly, to mistuning a concentric assembly to reduce vibrations.
Gas turbine engines are known and, typically, include a fan delivering air into a bypass duct as propulsion air and to be utilized to cool components. The fan also delivers air into a core engine where it is compressed in a compressor. The compressed air is then delivered into a combustion section where it is mixed with fuel and ignited. Products of the combustion pass downstream over turbine rotors, driving them to rotate.
One type of gas turbine engine has multiple bypass streams. In such engine, there is typically a radially outer third stream bypass flow and a radially inner main bypass flow. Other types of gas turbine engines have other bypass flow arrangements.
Gas turbine engines, and in particular gas turbine engines having multiple bypass streams, may include assemblies having a concentric airfoil arrays. These assemblies often have very little structural damping due to their symmetric nature. Lack of damping can lead to, among other things, high cycle fatigue issues resulting from high vibratory stresses, such as resonant or aero-elastic responses of the airfoils to dynamic pressure fluctuations. Mitigating these fatigue issues has involved increasing airfoil thicknesses, which can lead to localized hot spots and vibratory stresses and diminished aero-dynamic performance.